Conventionally, transparent electrodes have been used in various devices. A transparent electrode is generally placed on a transparent substrate or insulating layer. For example, Patent Literature 1 discloses an electrochromic multi-color display device 100 as shown in FIG. 4.
In the display device 100, a display substrate 11 and a counter electrode 12 are attached to each other via a spacer 18, and a cell is thus formed. In the cell, a first display electrode 13a, a first electrochromic layer 14a, an insulating layer 15, a second display electrode 13b, and a second electrochromic layer 14b are layered on the display substrate 11. A counter electrode 17 and a white reflective layer 16 are layered on the counter electrode 12. In addition, the inside of the cell is filled with an electrolyte 19.
The first display electrode 13a and the second display electrode 13b are transparent electrodes. The first electrochromic layer 14a is caused to produce a first color or to become colorless by control of the voltage applied between the first display electrode 13a and the counter electrode 17. The second electrochromic layer 14b is caused to produce a second color different from the first color or to become colorless by control of the voltage applied between the second display electrode 13b and the counter electrode 17.
The first electrochromic layer 14a and the second electrochromic layer 14b generally have a structure in which an electrochromic compound is supported on a metal oxide. The metal oxide used has conducting properties in some cases. The insulating layer 15 is intended to allow separate control of the potential of the first display electrode 13a and the potential of the second display electrode 13b. In addition, the insulating layer 15 is transparent, and is porous in order that the electrolyte 19 permeates into the insulating layer 15 so as to allow ion transfer associated with oxidation-reduction reaction.